Roller valve lifter

ABSTRACT

A roller valve lifter apparatus for following an eccentric cam in an internal combustion engine includes a cylindrical roller, configured to roll upon the eccentric cam, and a lifter body, having a curved roller socket configured to retain the roller and to allow rotation of the roller in the roller socket upon a layer of lubricating fluid trapped between the roller surface and a bearing surface of the roller socket. In one embodiment the roller socket includes tapered end portions defining distal gaps between the roller surface and the bearing surface, for allowing entry of splash oil therebetween.

The present application claims priority from U.S. Provisional PatentApplication Ser. No. 60/587,627, filed on Jul. 8, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to valve lifters for actuating push rods ininternal combustion engines. More particularly, the present inventionrelates to an improved roller valve lifter that requires no conventionalball bearing for the roller.

2. Related Art

Internal combustion engines typically comprise a pair or more of valvesassociated with each cylinder for intake and exhaust, which open andclose to take in fuel and air, and to allow exhaust gasses to escapefollowing combustion. These valves are typically opened and closed bythe rotation of a camshaft comprising a plurality of eccentric camsdisposed on a shaft which rotates synchronously with the engine.Associated with each valve is a valve lifter, which is in contact withone cam of the camshaft and aligned perpendicular thereto, so as totranslate rotational motion of the cam into axial reciprocal motion ofthe valve lifter. The lifter in turn is connected to a push rod, whichis connected to a hinged rocker arm assembly, which acts directly on thevalve. The entire valve lifter/push rod/rocker arm/valve assembly istypically biased in a closed position by a spring, to keep the valvelifter in contact with its associated cam.

One of the major sources of friction in such a driven valve train iscreated at the interface between the valve lifter and the cam. In veryearly internal combustion engines, valve trains were frequently actuatedby flat-ended, solid valve lifters, which were placed in sliding contactwith each cam. This construction was simple, but with production ofengines designed for higher operating speeds and having higher valvespring biasing forces, flat lifters became inadequate. In spite of theuse of sufficient lubricating oil, flat lifters experienced extremelyhigh wear of the cam lobe and lifter, and generated substantial heatfrom the friction. The cam lobe and lifter surface would be quickly worndown, introducing abrasive debris into the engine, and eventuallywearing the lifter to the point that the valve action would no longerallow the engine to run properly.

To address some of these problems, attempts were made many years ago toemploy valve lifters having a radius formed on the bearing end surface.However, even when hardened steel or chrome steel were used, thefriction-induced wear on the cam and lifter were found to be excessive.This condition was exacerbated by the difficulty of providing sufficientlubricating oil to the sliding surface. Consequently, these attemptswere generally unsuccessful, and radius lifters were long ago abandonedin favor of roller valve lifters.

Roller valve lifters employ a roller disposed at the bearing end of thevalve lifter that is in contact with the cam lobe. The current method ofproducing roller type valve lifters uses steel rollers centered aroundan axle, with a needle bearing, having an array of thin steel needlesset laterally and parallel around the axle, separating the axle from thewheel. Thus instead of sliding friction between the valve lifter and thecam, the roller valve lifter rolls over the cam lobe with far lessfriction. Unfortunately, the needle bearings and axles are frequentlyunable to withstand the high frequency, high impact load of the rotatingcam, and tend to fracture, spreading sharp metal debris throughout theengine. This is a main cause of frequent failures in roller bearingvalve lifters used in high-performance engines. Additionally, the wheel,axle, and other portions of typical roller valve lifters make themrelatively complicated, costly, and heavy.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop asimple, economical, and lightweight roller valve lifter that can reducefriction without experiencing excessive wear or causing excessive wearto the cam.

It has also been recognized that it would be desirable to have a rollervalve lifter that avoids the drawbacks associated with needle bearingsin typical roller valve lifters.

It has also been recognized that it would be desirable to have a rollervalve lifter which incorporates an improved system for transmittinglubricating oil to regions where it is needed.

In one embodiment, the invention provides a valve lifter apparatus forfollowing an eccentric cam in an internal combustion engine. The valvelifter includes a cylindrical roller, configured to roll upon theeccentric cam, and a lifter body, having a curved roller socketconfigured to retain the roller and to allow rotation of the roller inthe roller socket upon a layer of lubricating fluid trapped between theroller surface and a bearing surface of the roller socket. The rollersocket includes tapered end portions defining distal gaps between theroller surface and the bearing surface, for allowing entry of splash oiltherebetween.

In accordance with another embodiment thereof, the invention provides avalve lifter apparatus for following an eccentric cam in an internalcombustion engine. The valve lifter apparatus includes a lifter body,having a roller socket, a cylindrical roller, disposed in the rollersocket, and means for laterally retaining the roller in the rollersocket. The roller socket has a curved bearing surface defining an arcof greater than 180 degrees, and the bearing surface includes a circularcentral portion with a constant radius. The cylindrical roller includesa roller surface configured to roll upon the eccentric cam, and has aradius substantially equal to the radius of the circular central portionof the roller socket. The roller is configured for sliding bearing inthe roller socket upon lubricating fluid disposed between the rollersurface and the bearing surface.

In accordance with another more detailed embodiment thereof, the valvelifter includes a lubricant passageway in the lifter body, having anoutlet in the bearing surface, configured to allow a flow of lubricatingfluid to the region between the roller surface and the bearing surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention, and wherein:

FIG. 1 is a partial cross-sectional fragmented view of a typical valvelifter shown in operational relationship to the valve assembly of atypical internal combustion engine;

FIG. 2 is a side view of a typical prior art roller valve lifter;

FIG. 3 is a perspective view of one embodiment of a roller valve lifterin accordance with the present invention;

FIG. 4 is an exploded perspective view of the valve lifter assembly ofFIG. 3;

FIG. 5 is a perspective view of the internal lifter body;

FIG. 6 is a longitudinal cross-sectional view of the internal lifterbody of FIG. 5;

FIG. 7A is a cross-sectional view of the valve lifter assembly of FIG.3, taken along a plane that is perpendicular to the rotational axis ofthe roller;

FIG. 7B is a cross-sectional view of the valve lifter assembly of FIG.3, taken along a plane that is parallel to the rotational axis of theroller;

FIG. 8 is a close-up cross-sectional view showing the geometry of theroller and roller socket;

FIG. 9 is an exploded perspective view of another embodiment of a lifterbody and roller in accordance with the present invention; and

FIG. 10 is a perspective view of a roller valve lifter having analternative outer shell.

DETAILED DESCRIPTION

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features illustrated herein, andadditional applications of the principles of the inventions asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

FIG. 1 is a partial cross-sectional fragmented view of a typical valvelifter shown in operational relationship within the valve assembly of atypical internal combustion engine 10. The valve lifter 12 is disposedwithin a cylindrical valve lifter bore 14 with its lower end held incontact with a cam 16. The top of the valve lifter is connected to apush rod 18 which is connected to a rocker arm 20 which acts directly ona valve 22 which governs the ingress and egress of combustion reagentsand products with respect to a cylinder 24. As the cam rotates on itsshaft, its eccentric lobe 17 cyclically moves toward and then away fromthe end of the valve lifter. The contact of the end of the valve lifteron the surface of the rotating cam converts the rotational motion of thecam into axial reciprocal motion of the valve lifter, and consequentlythe valve. The entire valve lifter/push rod/rocker arm/valve assembly isbiased by coil spring 26, which acts to keep the bottom of the valvelifter in contact with the cam, and keeps the valve closed when the camlobe is rotated away from the end of the lifter.

FIG. 2 provides a more detailed side view of a prior art valve lifter 12comprising a roller assembly 30 at its lower end. The roller assembly isdesigned to engage the surface of the cam lobe 17 so as to convert therotational motion of the cam into axial reciprocal motion of the valvelifter, thence imparting the axial reciprocation to the push rod 18. Thepush rod is typically fitted into a socket 19 formed in a conical orother shaped recess 21 formed in the top of the valve lifter. Extendingfrom the center of the socket is a bleed oil conduit 23 which leads to ableed oil hole 25 formed in the side of the valve lifter. A smallpartition 27 is provided in the opening of the bleed oil hole toseparate it from the main oil flow. The bleed oil conduit is in fluidcommunication with a similar oil conduit 29 provided in the center ofthe push rod. This configuration advantageously feeds a relatively smallquantity of lubricating oil from the high oil pressure zone present inthe very small annular space between the outside surface 33 of thelifter and the valve lifter bore, up to the push rod/rocker armassembly.

Typical valve lifters 12 are also frequently provided with oiltransmission passages for allowing engine galley oil to flow from onevalve lifter to another along the valve train. Viewing FIG. 1, the oilgalley would typically extend perpendicular to the plane of the page(parallel to the cam shaft 16), and would intersect each valve lifterbore approximately at the average midpoint of each valve lifter. Toallow the galley oil to flow along the valve train, each valve lifter isprovided with oil transmission means. This may comprise an annularrecess or slot around the middle of each valve lifter, or may be atransverse conduit of various configurations formed through the middleof the valve lifter body. The prior art valve lifter shown in FIG. 2incorporates an oil transmission means comprising an annular recess orgroove 35 formed about its midsection. This allows the oil to flowbetween valve lifters, and also provides oil for each valve lifter andassociated components, including the cam and the valve lifter/pushrod/rocker arm/valve assembly.

The roller lifter assembly 30 typically comprises a wheel 32 having anaxle and needle bearings 34 attached to the valve lifter by a cradle orframe 36. Such rollers are well known, and have represented the state ofthe art for many years. Unfortunately, this configuration is relativelycomplicated and expensive because it involves many parts, and it tendsto be heavy because of the relatively stiff connection required for theroller assembly. Additionally, the wheel, axle, and needle bearings areprone to wear out, especially in high performance engines. The needlebearings and axles are frequently unable to withstand the highfrequency, high impact load of the rotating cam, and tend to fracture,spreading sharp metal debris throughout the engine. This is a main causeof frequent failures in roller bearing valve lifters used in highperformance engines.

Advantageously, the inventor has devised a roller valve lifter thatovercomes some of the problems of prior roller valve lifters. Oneembodiment of a roller valve lifter 100 in accordance with the presentinvention is shown in FIGS. 3-4. The valve lifter comprises threegeneral parts: an internal lifter body 110, a roller 112, and an outersleeve or shell 114. The roller is held within a roller well or socket116 that is transversely bored in the lower end of the internal lifterbody. The lower end of the roller extends through a roller opening 118located in the lower end of the outer shell.

The inventor's approach is a departure from prior valve lifters in thatit uses a solid roller having no center hole to accommodate an axle andsupporting needle bearings. Instead, the roller 112 is suspended on afilm of oil trapped within the roller socket 116. The roller floats asit spins on the trapped oil, making no direct contact with thecorresponding contour of the socket or roller well. This operation ofthe roller is made possible because liquids are incompressible,following the same principle that is applied in connecting rod bearings,which float on oil around a crankshaft journal, while making no directcontact with the crank journal.

The inner lifter body 110 is preferably lightweight, and includesfeatures for transmitting lubricating fluid. In one embodiment, theinner lifter body is made of hardened aluminum, which helps allow it toresist wear and high temperatures. Alternatively, the inner lifter bodycan be of steel, such as hardened steel. The inner lifter body can beconfigured in a variety of ways. One possible configuration is shown inFIGS. 4-7. Viewing FIGS. 5 and 6, the upper end of the inner lifter bodyincludes a conical recess 120 with a socket 122 that is configured toreceive a push rod with a radiused end. The cross-sectional views ofFIGS. 7A and 7B show a push rod socket 124 and push rod 126 (in dashedlines) installed in the socket. A vertical push rod lubricant passageway130 is provided in the center of the internal lifter body to allowlubricating oil to flow to the push rod via the socket. Those skilled inthe art will recognize that the push rod socket can be supported by ahydraulic piston assembly (not shown) that cushions the lifter impactand reduces the need for lash adjustment in the valve lifter/pushrod/rocker arm/valve assembly.

As shown in FIG. 7B, a horizontal push rod lubricant passageway 132interconnects the vertical push rod lubricant passageway with anexternal opening 134, that allows lubricating oil to enter. The externalopening of the horizontal lubricant passageway is disposed in an annulargroove 136 formed in the inner lifter body. This annular groove providesan oil transmission passage for allowing engine galley oil to flow fromone valve lifter to another along the valve train. As noted above, theoil galley would typically intersect each valve lifter boreapproximately at the average midpoint of each valve lifter. The annulargroove is provided to allow the galley oil to flow along the valve trainto each valve lifter. As shown in FIGS. 3, 4, and 7B, the outer sleeveor shell 114 includes oil flow openings 138 on each side that coincidewith the annular groove, and allow oil to flow from the galley oilpassages into the groove. This allows the oil to flow between and amongthe entire bank of valve lifters, and also provides oil for each valvelifter and associated components, including the cam and the valvelifter/push rod/rocker arm/valve assembly. It will be apparent thatother configurations for transmitting lubricating oil can also beprovided.

The inner lifter body 110 also includes two lubricating oil passageways140 that extend downward from the annular groove 136 to openings 142 inthe roller well/socket 116. The longitudinal portion 144 of thesepassageways comprises a groove formed in the outer surface of the innerlifter body. It will be apparent that when covered by the outer sleeve114 this groove becomes a closed passageway. The transverse portion 146of this passageway leads to the openings in the roller socket. Thesepassageways provide a path for lubricating oil to travel from theannular groove to the inside surface of the roller socket to lubricatethe roller.

Another embodiment of an inner lifter body 210 is shown in FIG. 9. Thisembodiment is configured to be less massive than that described above,while still including all essential functional elements and providingsufficient strength to withstand the forces it will experience. As withthe embodiment of FIGS. 3-7, this lifter body includes a roller well orsocket 216 that is transversely bored in the lower end of the internallifter body, in which the roller is configured to be suspended on a filmof trapped oil. The inner lifter body includes features for transmittinglubricating fluid. It includes a conical recess 220 and socket 222 thatare configured to receive a push rod bearing, with a vertical push rodlubricant passageway (not shown) to allow lubricating oil to flow to thepush rod bearing.

The inner lifter body 210 includes a very large annular groove 236 whichprovides an oil transmission passage for allowing engine galley oil toflow from one valve lifter to another along the valve train, in themanner discussed above, and can also include a passageway fortransmitting oil to the vertical push rod lubricant passageway. Theinner lifter body also includes lubricating oil passageways 240 thatextend downward from the annular groove to openings 242 in each side ofthe roller well/socket 216, and are generally configured like thecomparable structure of the lifter body embodiment described above.These passageways provide a path for lubricating oil to travel from theannular groove to the inside surface of the roller socket to lubricatethe roller. The following discussion of the roller and roller socket,though specifically referring to the inner lifter body 110 of FIGS. 4-8,applies equally to the inner lifter body of FIG. 9.

Referring back to FIGS. 3-8, the roller 112 is a substantially solidcylindrical body of a suitable material that is configured to rotatewithin the roller socket 116. As shown in FIG. 8, the roller socketdefines an arc a of greater than 1800, so that the bearing surface 148of the socket wraps around the roller to hold it in place. The rollersocket has a curvature that allows the roller to rotate in the socketagainst a thin film of lubricating oil trapped between the rollersurface and the bearing surface of the socket, creating a lubricationzone. Advantageously, the trapped lubricating oil directly supports thespinning roller with very little friction, and is not forced out duringthe rapid high pressure impact of the roller within the socket with eachrotation of the cam. This is due in part to the fact that liquids areincompressible, and because each impact is so rapid that the lubricatingoil simply cannot flow out of the way fast enough.

This solid roller configuration provides advantages over some prior art.Roller valve lifters having a hollowed steel roller running against asaddle of plastic bearing material have been proposed. Unfortunately,these lightweight materials do not provide sufficient rigidity toprevent loss of conformity between the roller and the saddle. This canallow the elimination of the hydrostatic film of oil separating theroller and the saddle under high loads, causing undesirable contact ofthe two surfaces. In contrast, testing has demonstrated that the solidroller of the present valve lifter, saddled in the hardened inner lifterbody, does not experience substantial deformation and a resultant lossof the hydrostatic film of lubricating oil, thus maintaining separationof the two surfaces even under extremely heavy loads.

One aspect of the present invention is the use of a roller having a veryhigh modulus of elasticity so as to have very little flexure. In oneembodiment, the roller 112 is made of Silicon Nitride (SiNi), a veryhard and lightweight composite ceramic material that is commerciallyavailable from a variety of sources. The solid composite roller isadvantageous in comparison with many steel rollers. A steel roller ofsimilar material and similar hardness to a cam lobe has a tendency togall and/or pick up metal as the roller is accelerated onto the openingramp (150 in FIG. 7A) of a cam lobe. This galling of the surfaces cantransfer small particles of metal to the surface of the bearing that theroller rides in, thus scratching or scoring this surface, and providingescape pathways for the lubricating oil. This hinders the operation ofthe “trapped oil” concept.

Advantageously, a composite roller, having a much greater hardness thanthe cam lobe, maintains a higher degree of its polished finish forlonger lasting, non-galling relationship with the cam lobe. The hardnessof the composite ceramic roller material also allows it to accept andmaintain an extremely smooth finish to prevent wear to both the cam lobeand the lifter's bearing surface, thus helping to prevent scoring. Ahighly polished silicon nitride surface will not scratch like mostgrades of steel. Contact between silicon nitride and steel or cast ironwill tend to simply polish the metal, without picking up particles thatcan scratch or score the roller well, which can be of aluminum.

Additionally, a composite roller, having considerably greater stiffnessthan a steel roller of comparable configuration, retains its shapebetter, and thus conforms better to the precision matching radius of thebearing surface 148 of the roller well 116 without distortion orburnishing from the extreme pressure brought on by the valve springs ofhigh performance engines. The hard, polished ceramic roller retains itsshape better, and thus the roller and the roller well maintain theirability to trap oil.

The light weight of the composite roller 112 also aids in theacceleration of the roller against the spinning camshaft lobe. That is,the roller will speed up and slow down significantly with each rotationof the cam shaft. Advantageously, the lighter weight composite rollerpresents lower inertial forces, and thus requires less energy to changeits velocity with each revolution. This helps make the engine moreefficient.

While silicon nitride is a very suitable material for the roller, it isbelieved that other materials can also be used in the present invention.For example, steel of suitable hardness (e.g. heat-treated steel) orother metals could also be used, so long as the modulus of elasticityand shape are such as to resist flexure or deformation that could hinderconformity of the roller and roller bearing socket. One grade of steelthat may be suitable is 52100 steel.

In some applications, a steel roller may be preferred for its lower costwhere the operating conditions are not so intense and the superiorcharacteristics of the ceramic material are not required. Alternatively,for example, in more severe operating conditions, a steel roller mightbe used where a racing association's rules require the use of a rollerlifter, but prohibit the use of ceramic materials. In such cases, theshortened life may be acceptable since it need last only for theduration of the race, and would normally be replaced when the engine isrebuilt for the next event. In short, while a ceramic roller with ahardened steel lifter body is one desirable configuration, othercombinations of materials can be used where other considerations such ascost or association rules make this desirable. This would allow theadvantages of the invention—reduced friction without the use ofunreliable axles and needle bearings—to be retained even when, for otherreasons, the ceramic roller could or would not be used.

The outer shell or sleeve 114 can be made of hardened steel, and can befabricated in various ways. In on embodiment, the inventor has machinedthe outer shell from a solid piece of bar stock. Alternatively, theinventor has manufactured the outer shell from tubing of a suitable sizeand grade. Other suitable manufacturing techniques can also be applied.The outer shell can be attached or affixed to the inner lifter body invarious ways. For example, the outer shell can be bonded to the innerlifter body with a suitable adhesive, such as an epoxy. Alternatively,dowel pins can be provided to mechanically affix the sleeve to the innerlifter body.

The outer shell or sleeve 114 performs several functions in the rollerlifter assembly. First, the shell is fixed permanently as a cover forthe inner lifter body 110, and provides a wear-resistant outer surfacefor the lifter in its lifter bore. For example, where the inner lifterbody is of aluminum, a hardened steel outer shell will provide greaterwear resistance. Second, the outer shell also operates as a retainer, toenclose and center the roller 112, restricting the roller's lateralmovement. The shell can also include flattened side faces or facets 115on opposing sides near the push rod end, for mating with a non-circularshape in a portion of the valve lifter bore. Such a configuration issometimes used for preventing rotation of lifters within their lifterbores, to ensure that the axis of rotation of the roller remainsparallel to the axis of rotation of the camshaft.

In the embodiment shown in FIGS. 3-7, the roller opening 118 of theouter shell includes side surfaces 152 that are disposed adjacent to thevertical sides 154 of the roller. If the roller drifts laterally as itrotates within the socket 116, its sides will contact the sides of theroller opening of the hardened steel outer shell, and thus be preventedfrom further drift. This centers and retains the roller in the innerlifter body, and also prevents the outer corner radius surface 156 ofthe roller from making contact with the inside wall of the steel shell,while still keeping the roller centered on the cam lobe.

The steel shell 114 also helps support the integrity of the rollersocket 116 in the inner lifter body 10. That is, because the innerlifter body and the bore surrounding the roller leaves a relativelysmall thickness of material for holding the roller, the added structureof the steel outer shell helps provide strength and stability to theroller socket. Advantageously, the roller opening 118 in the steel outerbody is smaller in length L than the diameter D of the roller 112, andthus provides backup structure to prevent the roller from escaping fromthe roller well. By having a length dimension that is shorter than thediameter of the protruding roller, the roller cannot escape, even if theinner body surrounding the roller socket were to crack or break.

In the embodiment depicted in FIGS. 3-4 and 7, the outer shell 114includes flattened side portions 161 at the roller end on either side ofthe roller, with windows 162 in these side portions. This configurationprovides several functions. The flattened side portions on each lateralside of the roller are provided to reduce the overall width of thelifter on the roller end, so as to provide clearance for neighboring camlobes and other obstructions that may exist in the cylinder block. Giventhat the shell is a hollow cylinder, machining these flattened sideportions has the effect of creating the windows. Advantageously, thewindows provide an escape route for oil that is flushed from the rollerwell. That is, when the roller well is provided with pressurized oilfrom the lifter galley via the lubricating oil passageways 140, thispressurized flow will generally create an outflow of hot oil from theroller well region. The windows help provide a pathway for the escape ofthis oil.

In one aspect, the roller valve lifter 100 can function with only splashoil. This is particularly desirable because some engines do not haveengine oil pressure feeding the lifter galley. Those of skill in the artwill recognize that splash oil is flung about by centrifugal force fromthe rotating elements of the crankshaft and camshaft assemblies. Usingonly this splash oil is possible because the valve lifter provides anentry path at the bottom of the lifter, facing the crankshaft, forsplash oil to be channeled into the space between the roller and theroller well. Specifically, the shape of the roller socket 116 isconfigured to provide a gap 160 between the roller 112 and the socket atthe lower extremity of the roller. This gap allows splash oil to bedrawn between the roller and the bearing surface 148 of the rollersocket, to provide a cushion or boundary layer and to lubricate and coolduring rotation of the roller. Additionally, the windows 162 in theouter shell 114 can also provide a pathway to allow splash oil to enterthe roller well region, though this is not believed to be a majorcontributor to the introduction of splash oil.

The oil gap 160 is created by the shape of the roller well 116, shown inan exaggerated view in FIG. 8. The bearing surface 148 of the rollerwell has three distinct sections. First, it has a circular centralportion 164 with a constant radius that substantially matches the radiusof the roller 112. This matching radius is substantially the same,within machining tolerances, as the radius of the roller, so that a thinfilm of lubricating oil can be trapped between the two surfaces. Thisconstant radius portion of the bearing surface provides a compressionzone, wherein most of the force exerted by the cam on the roller istransferred to the inner lifter body 110. In the embodiment depicted inFIG. 8, the compression zone defines an arc P of about 130° to 140°,though the arc length can vary from this.

The roller well 116 also includes two tapered end portions 166 thatprovide the oil gaps 160 at their lower extremities between the roller112 and the bearing surface 148. The gap shown in FIG. 8 is greatlyexaggerated in size in order to show its configuration. In oneembodiment, the tapered end portions define spiral or non-circularcurves, having curved surfaces of gradually increasing radius from theends of the compression zone to the lower end of the lifter body. Anapproximate spiral curve can be created by boring one or more largerdiameter bores, each slightly larger (by only a few thousands of aninch) than the previous hole, but centered below the previous bore, withsmall tangent surfaces between each adjacent curve. Because they have alower center, the larger bores will not conflict with the main bore (theone that defines the circular central portion of the roller well), butwill widen the lower region of the roller well. Other curve shapes, suchas parabolic, semi-elliptical, etc., can also be used to shape theroller well to provide the oil gap.

This spiral shape creates the gap 160 that allows splash oil to bechanneled into the compression zone 164. This is a great advantage incomparison with some other prior art valve lifters. Some prior art valvelifters have closed edge openings that tend to scrape the oil from theroller. This design, in contrast, allows splash oil to be drawn betweenthe roller and the bearing surface by the rotation of the roller, toform a boundary layer acting as a cushion between the roller and thebearing. Because the liquid oil is incompressible, like fluidsgenerally, it will not be able to squeeze out of the compression zonebetween the roller and the bearing surface in response to the rapidimpact of the cam lobe 150 against the roller 112, thus maintaining theneeded separation and a highly lubricated condition.

However, splash oil lubrication is not the only lubrication methodanticipated by this roller valve lifter. As noted above, the innerlifter body 110 includes lubricating oil passageways 140 that extenddownward from the annular groove 136 to openings 142 in the rollerwell/socket 116. The openings in the roller socket provide a path forlubricating oil to travel from the annular groove to the inside surfaceof the roller socket to lubricate the roller. As shown in FIG. 8, theopenings of these passageways are located in the tapered end portions166 of the roller well, outside the compression zone 164. It will beapparent that if the openings were in the compression zone, pressurefrom the roller would tend to force oil out of the compression zone andback into the oil passageways, rather than allowing the oil passagewaysto supply oil to be trapped between the roller and the bearing surface148, as intended.

Advantageously, the oil passageways 140 and the gaps 160 at the bottomof the roller well 116 also provide a pathway for hot oil to escape fromthe compression zone. This allows oil to enter the compression zone, tocushion the impact, lubricate, and cool the roller for a time, and thenescape to be recirculated. This prevents oil from remaining in thecompression zone too long and becoming too hot. Hot oil does notlubricate as well, and can chemically break down, thus allowingundesired contact and wear of the surfaces. However, when oil isproperly circulated, it is allowed to cool properly and perform itsintended function much better.

Another embodiment of an outer shell 214 is shown in FIG. 10. Thisembodiment of the outer shell can be used with any of the embodiments ofthe inner lifter body shown and described herein. This embodiment of thesleeve or shell includes features comparable to those described abovewith respect to the embodiment of FIGS. 3-4 and 7. It includes oil flowopenings 238 on each side to allow oil to flow between and among anentire bank of valve lifters, and also to provide oil internally foreach valve lifter and associated components, including the cam and thevalve lifter/push rod/rocker arm/valve assembly. It also includes adrilled hole 262 for allowing the sleeve to be mechanically dowel-pinnedto the inner lifter body. The portions of the shell that are disposedadjacent to the ends of the roller socket (that is, near the oil gap 260adjacent the bearing surface of the roller) are also configuredsubstantially like the shell embodiment of FIGS. 3-4 and 7 and functionin substantially the same way.

Advantageously, the shell 214 of FIG. 10 includes tapered side portions252 that converge into roller socket side panels 254. This tapered shapeprovides several advantages. First, it reduces the overall width of thelifter at the roller end, so as to provide clearance for neighboring camlobes and other obstructions that may exist in the cylinder block.Additionally, the side panels are located adjacent to the vertical sidesof the roller, and operate to center the roller and laterally keep it inits socket. The clearance between the side panels of the shell and theside surfaces of the roller can be large enough to allow the escape ofoil from the roller well, and yet small enough to keep the roller wheelproperly centered. In one embodiment, the inventor has provided aclearance of about 0.010″ between the side panels of the shell and thesides of the roller. Because it provides larger surfaces and is ofcontinuous material, this configuration gives the shell greater sidethrust strength for keeping the roller centered than does the embodimentof FIGS. 3-4 and 7. Specifically, rather than a very small edge surfacethat contacts the sides of the roller (e.g. side surfaces 152 of theroller opening 118 in FIG. 4), this configuration places the entire sidepanel against the side of the roller, providing additional surface areaand more material to resist lateral forces. Additionally, the absence ofwindows in the shell (like the windows 162 in FIGS. 3-4 and 7) in theregion of the roller well also provides greater strength.

Advantageously, the shell embodiment 214 of FIG. 10 can be fabricatedfrom tube stock, and requires less labor to produce than the embodimentof FIGS. 3-4 and 7. The tube stock, which can be less expensive tomachine than bar stock, is tapered at the roller end in a punch pressoperation to form the desired shape, then, after assembly of thecomplete lifter, is ground on its outer surface to ensure the properdiameter and roundness and to provide a smooth outer surface. Thisprocess involves fewer steps and produces a stronger part with lesswaste than the use of bar stock, and can be significantly less expensiveoverall.

By way of example, and without limitation, the invention can bedescribed as providing a valve lifter apparatus for following aneccentric cam in an internal combustion engine. The valve lifterincludes a solid cylindrical roller configured to roll upon theeccentric cam, a lifter body having a roller socket configured tocontain the roller, and a retainer configured to laterally retain theroller in the roller socket. The roller socket has a bearing surfacedefining an arc of greater than 180 degrees, having a circular centralportion with a constant radius substantially equal to the radius of theroller, and tapered end portions defining distal gaps between the rollerand the bearing surface. The distal gaps are configured for allowingentry of lubricating fluid between the roller and the bearing surface.The roller is configured for sliding bearing in the roller socket upon alayer of lubricating fluid disposed between the roller surface and thebearing surface of the roller socket. The retainer can be configured toallow splash oil from a cam shaft associated with the eccentric cam toreach the distal gaps between the roller and the bearing surface, forallowing entry of lubricating fluid therebetween.

As a more detailed example, the valve lifter can include a lubricantpassageway in the lifter body, having an outlet in the bearing surfaceof the roller socket outside the circular central portion, configured toallow a flow of lubricating fluid to the region between the rollersurface and the bearing surface. More particularly, the lubricantpassageway can extend to an inlet in fluid communication with an oilgalley configured for transmitting lubricating oil between a pluralityof valve lifters.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

1. A valve lifter for following a rotating eccentric cam, comprising: asolid cylindrical roller, having a radius and a roller surfaceconfigured to roll upon the eccentric cam; a lifter body, having aroller socket configured to contain the roller, the roller socket havingan arcuate bearing surface including a circular portion with a constantradius substantially equal to the radius of the roller, and tapered endportions diverging from the constant radius and defining distal gapsbetween the roller and the bearing surface, the roller being configuredfor sliding bearing in the roller socket upon lubricating fluid disposedbetween the roller surface and the bearing surface; and a retainer,attached to the lifter body, configured to laterally retain the rollerin the roller socket.
 2. A valve lifter as defined in claim 1, whereinthe bearing surface of the roller socket defines an arc of greater than180 degrees.
 3. A valve lifter as defined in claim 2, further comprisinga lubricant passageway in the lifter body, having an outlet in thebearing surface of the roller socket, configured to allow a flow oflubricating fluid to the region between the roller surface and thebearing surface.
 4. A valve lifter as defined in claim 3, wherein thelubricant passageway extends to an inlet in fluid communication with anoil galley configured for transmitting lubricating oil between aplurality of valve lifters.
 5. A valve lifter as defined in claim 3,wherein the outlet of the lubricant passageway is disposed outside thecircular portion.
 6. A valve lifter as defined in claim 1, furthercomprising a lubricant passageway in the lifter body, having an outletin the bearing surface of the roller socket, configured to allow a flowof lubricating fluid to the region between the roller surface and thebearing surface.
 7. A valve lifter as defined in claim 6, wherein thelubricant passageway extends to an inlet in fluid communication with anoil galley configured for transmitting lubricating oil between aplurality of valve lifters.
 8. A valve lifter as defined in claim 1,further comprising an oil transmission passageway, disposed in thelifter body, configured to allow lubricating oil of an oil galley toflow to and past the valve lifter.
 9. A valve lifter as defined in claim1, wherein the retainer is configured to allow splash oil from a camshaft associated with the eccentric cam to reach the distal gaps betweenthe roller and the bearing surface, for allowing entry of lubricatingfluid therebetween.
 10. A valve lifter as defined in claim 1, whereinthe retainer comprises a metal sleeve, disposed about the lifter body.11. A valve lifter as defined in claim 1, wherein the retainer is bondedto the lifter body with an adhesive.
 12. A valve lifter as defined inclaim 1, wherein the retainer comprises side surfaces disposed adjacentto opposing flat sides of the roller, configured to laterally retain theroller in the roller socket.
 13. A valve lifter as defined in claim 1,wherein the retainer comprises tapered side portions which converge intoroller socket side panels, the side panels being located adjacent toopposing flat sides of the roller and configured to laterally retain theroller in the roller socket.
 14. A valve lifter as defined in claim 1,wherein the roller comprises a composite ceramic material.
 15. A valvelifter as defined in claim 14, wherein the roller comprises siliconnitride.
 16. A valve lifter as defined in claim 1, wherein the lifterbody comprises aluminum.
 17. A valve lifter apparatus for following aneccentric cam in an internal combustion engine, comprising: a lifterbody, having a roller socket with a curved bearing surface defining anarc of greater than 180 degrees, the bearing surface including acircular central portion with a substantially constant radius; acylindrical roller, disposed in the roller socket, having a rollersurface configured to roll upon the eccentric cam, and having a radiussubstantially equal to the radius of the circular central portion of theroller socket, the roller being configured for sliding bearing in theroller socket upon lubricating fluid trapped between the roller surfaceand the bearing surface; and means for laterally retaining the roller inthe roller socket.
 18. A valve lifter as defined in claim 17, whereinthe cylindrical roller is substantially solid.
 19. A valve lifter asdefined in claim 17, wherein the means for laterally retaining theroller in the roller socket comprises a metal sleeve, disposed about thelifter body, the metal sleeve having surfaces disposed adjacent to flatsides of the roller, and configured to laterally retain the roller inthe roller socket.
 20. A valve lifter apparatus for following aneccentric cam in an internal combustion engine, comprising: acylindrical roller, having a roller surface configured to roll upon theeccentric cam; and a lifter body, having a curved roller socket with abearing surface, the roller socket configured to retain the roller andto allow rotation of the roller in the roller socket upon a layer oflubricating fluid trapped between the roller surface and the bearingsurface, the roller socket having tapered end portions of increasingradii defining distal gaps between the roller surface and the bearingsurface, for allowing entry of splash oil therebetween.